Here’s a program to fix that:
Unlocker: http://ccollomb.free.fr/unlocker/
I’ve used this one and it’s very easy. Secondary click on your drive in explorer and hit “Unlocker” from the in context menu. It’ll tell you what processes are using it and even has a button to kill them.
I’ve heard this one mentioned as well, but I haven’t tried it: safelyremove http://safelyremove.com/
Sidenote: Here’s a good thread on tomshardware about ’safe removal’: http://www.tomshardware.com/forum/236841-31-safely-remove-hardware
